Study On The Regulation Of Surface Oxygen Species Of Manganese Oxide And Its Effect On The Catalytic Combustion Performance Of Toluene

Toluene,a typical representative of benzene series of aromatic hydrocarbons in volatile organic pollutants（VOCs）,threatens the safety of human environment.Among all kinds of toluene treatment technologies,catalytic combustion technology has attracted much attention due to its high purification efficiency and no secondary pollution.It is crucial to develop a low-cost catalyst with high thermal stability and good catalytic activity for catalytic combustion.Manganese oxides have a good capacity of oxygen storage and oxygen release,widely applied in catalytic combustion.However,the stability and activity of single manganese oxides remain to be improved.As a significant role in the M-V-K mechanism of catalytic oxidation of toluene,surface oxygen is considered as one of the ways to regulate the catalytic activity.Therefore,we regulated the content of manganese oxides and the annealing temperature to improve the catalytic performance of toluene,and further explored the influence of oxygen species change on the catalytic oxidation of toluene.The manganese oxide catalyst was modified by CeO₂-ZrO₂.The effect of MnOx content on the performance of CeO₂-ZrO₂-MnO_x catalyst was investigated by adjusting the content of manganese oxide.The result ofO₂-TPD showed that the surface oxygen species were in large numbers when the content of manganese was 60%(CZM_0.6),and the abundant oxygen species desorbed at low temperature availed the superior catalytic performance of the catalyst.At the same time,a distinct characteristic diffraction peak of oxygen vacancy was detected in CZM_0.6 catalyst by Raman.In addition,it was proposed that the change of surface oxygen species was caused by the synergistic effect between metals,deriving from the content of MnO_x.With increasing the Mn content,a volcanic tendency in H₂-TPR was observed.The resulting CZM_0.6 catalyst showed the strongest metal-metal interaction among all the catalysts,which weakened the metal-O and facilitated the escape of surface oxygen species It was beneficial to promote the catalytic oxidation of toluene.The CuO-MnO_x catalysts annealed at different temperatures were prepared to regulate the surface oxygen species and applied for the catalytic oxidation of toluene.It was found that with the increase of annealing temperature,the toluene conversion improved initially but then reduced.The catalyst annealed at 500℃ showed the best toluene oxidation performance,and T₁₀₀ was only 230℃.The results of XPS,Raman and H₂-TPR proved that the O_latt/O_ads ratio and the synergistic effect of metals were enhanced during the annealing temperature of 300-500℃,while a slight decline was observed beyond 500℃.Thereby,abundant lattice oxygen and strong synergistic effect between CuO and MnO_x in CM-500 contributed to its superior toluene oxidation performance.Moreover,a mechanism pathway was proposed based on the in-situ DRIFTS results.The initial step was the adsorption of toluene on catalyst,then the benzoic acid was rapidly converted to phenol and maleate in the presence ofO₂,then the intermediates were further oxidized to CO₂ and H₂O by reacting with the supplementary surface lattice oxygen.In this paper,we regulated the surface oxygen on MnO_x by varying the content of manganese oxides and the annealing temperatures,respectively.The relationship among the surface oxygen species,redox performance,metal-metal interaction,and the catalytic performance of toluene catalytic oxidation was analyzed.It was proposed that benzoate species were important intermediates in the catalytic oxidation of toluene based on M-V-K mechanism.We improve the catalytic performance of manganese-based catalyst for VOCs catalytic oxidation,which has practical and supportive significance for the technology popularization.